Conventionally, the first step in processing soybeans has involved the use of organic solvent extraction to remove oil from flakes of cleaned and cracked soybean meats. Hexane is a commonly used solvent for this purpose. The hexane is then separated from the oil and reused, leaving the oil as one of the desired products. Defatted flours and grits are then made from the extracted solids by desolventizing, grinding and screening. Defatted flours and grits are used in animal feeds, and are also the starting materials for further processing into protein concentrates and isolates. The production of protein concentrates has involved slurrying defatted flour in water at a pH of about 4.6, and separating solids and liquid centrifugally. The solids can be reslurried with water and again separated centrifugally. A third slurrying has also been suggested, followed by centrifugal separation, addition of caustics to the solids to bring the pH to 6.5-7.1, heating at 140.degree. F. for about thirty minutes, and then recovering a protein concentrate containing 68 percent protein and 4 percent water by spray drying.
Protein isolate has been produced from defatted soybean flour by slurrying the flour in water, adding caustic to adjust the pH to one in the range of 7-11, separating solids from the aqueous phase centrifugally, adjusting the pH of the aqueous phase to 4.5, recovering solids from the resulting slurry centrifugally, reslurrying the solids, recovering the reslurried solids centrifugally, adding caustic to a pH in the range of 6.5-7.0, and recovering protein isolate containing 92.5 percent protein and 5 percent water by spray drying.
These known ways for processing soybeans are discussed in considerable detail in FCS (Farmer Cooperative Service) Research Report 33, January, 1976. This Research Report is entitled "Edible Soy Protein".
Recently, it has been found that protein and oil can be recovered simultaneously in an aqueous system from raw peanuts and from fresh coconuts. Briefly, the process involves forming an aqueous slurry of the raw peanut or of the fresh coconut meat, separating solids from the slurry, three-phase centrifugation to recover an oil stream, an aqueous stream and solid material, demulsification of the oil, if required, and drying of the recovered protein. The pH of the initial slurry of raw peanuts or fresh coconuts is adjusted either to the alkaline side or to the acid side. At an alkaline pH the protein is dissolved, so that the initial separation of solids, e.g., by screening, removes most of the residue from the slurry, leaving the protein in solution. The protein can then be precipitated by acidifying the liquid phase, separating protein by a screening operation, and then subjecting the remaining liquid to three-phase centrifugation. The protein recovered by screening is then combined with the solids phase from the three-phase centrifugation and dried, constituting a protein isolate.
When the initial aqueous slurry is adjusted to an acid pH, the initial separation of solids removes most of the protein from the slurry, along with other insoluble materials. These solids are ultimately combined with the solids from the three-phase centrifugation, and the combined solids are dried, producing a protein concentrate.
These processes for simultaneous recovery of oil and protein from raw peanuts and fresh coconut are described in recent Journal articles, e.g., Cater et al, J. Amer. Oil Chem. Soc. 51:137 (1974); Rhee et al, J. Food Sci. 37:90 (1972); and Rhee et al, J. Food Sci. 38:126 (1973).